Vehicle fuel economy may be extended by stopping an internal combustion engine of the vehicle during vehicle stops. Instead of continuing to consume fuel at idle conditions where limited amounts of useful work may be done, an engine may be stopped so as to conserve fuel until vehicle motion or acceleration are desired. Of course, the vehicle engine may be stopped and started via dedicated operator engine stop and engine start requests. However, a vehicle operator may soon tire of inputting engine stop and start requests.
Another way to conserve fuel by stopping the engine includes automatically stopping and starting the engine absent dedicated operator initiated engine stop and engine start requests or commands. However, if an engine is automatically stopped and started, precise engine speed control during engine start and run-up to idle speed may be desirable to reduce transmission of engine torque to vehicle wheels. Nevertheless, precise engine speed control during engine start and run-up may be particularly difficult to achieve because the engine intake manifold is at or near atmospheric pressure during an engine start. Consequently, engine cylinders may induct a large air charge that requires a corresponding increase in fuel charge to reduce maintain stoichiometry for improved efficiency of the exhaust after treatment system. As a result, engine speed may increase to a level where an increased amount of engine torque may be transferred through a transmission torque converter and to vehicle wheels. The amount of speed and torque increase may be reduced with spark retard, but combustion stability and other factors may limit the amount of spark retard that may be applied. Additionally, a way of controlling cylinder air charge during an automatic engine start may not be suitable for an operator directed engine start because different masses may be coupled to the engine during an automatic engine start as compared to an operator directed engine start.
The inventors herein have recognized the above-mentioned limitations and have developed a method of starting an engine, comprising: positioning an air inlet throttle for an engine start; during an operator directed engine start, positioning a port throttle in a first position, the port throttle positioned downstream of the air inlet throttle in an air intake system of the engine; and positioning the port throttle in a second position during an automatic engine start, the automatic engine start not requested directly by an operator.
By adjusting port throttles and by providing different port throttle adjustments during operator and automatic starts, it may be possible to improve cylinder air charge control during engine starting. For example, port throttles may be partially opened during automatic engine starts to limit cylinder air charge, thereby controlling engine speed during engine starting and run-up (e.g., the period between engine cranking and when the engine reaches idle speed). The same port throttles may be opened further during an operator directed engine start so that engine speed may increase more rapidly during conditions where engine torque is less likely to be transmitted to vehicle wheels. In this way, port throttles may be adjusted to improve automatic and operator directed engine starts.
The present description may provide several advantages. For example, the approach may provide more precise engine speed control during automatic engine starting. Further, the approach may provide robust engine run-up during operator directed engine starting by allowing additional air to flow to the engine as compared with during automatic engine starts. Further still, in some examples, the approach may allow port throttles to be controlled in response to transmission operating conditions, thereby accounting for different masses that may be coupled to the engine during automatic and operator directed engine starts.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.